This example checks to see if the first list in the active document is a simple numbered list. If it is, the fourth list template on the Numbered tab of the Bullets and Numbering dialog box is applied.
Set myList = ActiveDocument.Lists(1)
If myList.Range.ListFormat.ListType = wdListSimpleNumbering Then
myList.ApplyListTemplate _
ListTemplate:=ListGalleries(wdNumberGallery) _
.ListTemplates(4)
End If